This invention relates to a valve structure which has a movable valve member that controls fluid flow through a flow passage and is designated particularly for resistance to high temperatures and being subjected to a fire.
In light of the recent emphasis placed upon safety, the utilization of valves which do not leak or fail when subjected to a fire is highly desirable. In pipelines which convey fluid such as petroleum products, a valve must have the capability to be tightly sealed in a closed position, and in the event of fire, the valve member must remain tightly sealed in a closed position even though the valve seals or sealing rings may be destroyed or impaired by fire.
Heretofore, fire-safe valve structures have been provided in which the valve sealing ring which contacts the movable valve member, such as a ball valve member, is backed by a fusible material which prevents displacement of the sealing ring until the material melts at a predetermined temperature and passes through a metering opening. U.S. Pat. No. 4,160,460 issued to Kemp for a "Fire-Safe Valve Structure" on July 10, 1979, is exemplary of this kind of structure. With respect to this type of structure, the incomplete melting of the fusible material or the failure of the fusible material to completely pass through the metering opening has prevented the sealing ring from being pushed completely into the seat pocket. Consequently, the opportunity exists for the sealing ring to interfere with the formation of an effective metal-to-metal seal between the valve member and the valve body. Further, if the downstream sealing ring is not fully pushed into the seat pocket, the valve member may not move a sufficient distance downstream and the upstream sealing ring may not be sufficiently unloaded to evacuate excessive body pressure into the flow pasage. The failure to evacuate excessive body pressure could result in severe damage to the valve. Thus, it would be highly desirable to provide a valve structure wherein the sealing ring is consistently pushed fully into the seat pocket when the valve structure reaches a predetermined temperature.
Production costs associated with a valve structure such as that shown in U.S. Pat. No. 4,160,460 are relatively complicated and costly. The metering openings must be drilled to communicate with the seat pocket, and the fusible material must be positioned in the seat pocket and machined to a proper size therein. Thus, it would be highly desirable to provide a fire-safe valve which can be made without these costly production operations.